On Monday, 1 October 2012 at 08:04:49 UTC, Jonathan M Davis wrote:
And you _can't_ determine ahead of time which functions can be
safely executed at compile time either, because that's an
instance of the halting problem.
I don't understand (I did read what "halting problem" means just
now, but I still don't understand). If there was no __ctfe
variable, and thus a guarantee that all functions do the same
thing at compile-time and run-time, couldn't the compiler just
try aggressively to execute all function calls at compile-time?
Obviously it wouldn't bother trying CTFE for function calls that
had arguments which weren't evaluable at compile-time. Nor would
it bother with functions that it knows have memory allocations or
other limitations of CTFE.
If not a compiler flag, then it could be a function attribute.
Just like c++ function attribute constexpr, which guarantees that
the function executes at compile time given you provide it with
compile-time evaluable arguments (and there are limitations to
what the function can do). Why wouldn't this attribute be
possible with D?
